Acrylic resins are excellent polymers used in large amounts in various industrial fields for their excellent transparency, color, appearance, weather resistance, luster, and processability. However, an essential disadvantage of acrylic resins is their poor impact resistance. As general methods for improving the impact resistance of an acrylic resin, various methods have been proposed in which a multilayer structure polymer having a rubber layer is introduced into an acrylic resin to form a two-phase structure to develop strength.
As an example of such a multilayer structure polymer introduced to improve impact resistance, Patent Literature 1 discloses a three-layer structure obtained by polymerizing an innermost layer mainly containing methyl methacrylate, then polymerizing a second layer mainly containing butyl acrylate in the presence of the innermost layer, and further polymerizing an outermost layer mainly containing methyl methacrylate.
However, when a multilayer structure polymer having a large particle diameter is mixed to improve impact resistance, the transparency of a resulting molded article is impaired. On the other hand, when a multilayer structure polymer having a small particle diameter is mixed, a resulting molded article has excellent transparency but its strength is low. For this reason, there has been a demand for a multilayer structure polymer excellent in both impact resistance and transparency.